added submission for desmondw

desmondw-assign1/caesar-cipher.txt

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+SBWKRQ

desmondw-assign1/caesar-plain.txt

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+PYTHON

desmondw-assign1/crypto.py

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+"""
+Assignment 1: Cryptography
+Course: CS 92SI
+Name: Desmond Chan 
+Date: 10/8/15
+
+This is a cryptography suite, where users can choose to encrypt or decrypt either strings or files using one of 3 methods:
+1. Caesar, which shifts letters by certain number of spaces in the alphabet
+2. Vigenere, which shifts letter by varying number of spaces in the alphabet according to a passkey
+3. Railfence, which draws out the word in a zig-zag pattern and reads the result row by row.
+"""
+
+def encrypt_caesar(plaintext):
+    """
+    Encrypts plaintext using a Caesar cipher.
+    First the plaintext is converted in upper case. Then according to the encryption dictionary,
+    it maps each letter from the original plaintext to its encrypted letter. It then returns
+    the new string.
+    """
+    plaintext = plaintext.upper()
+    caesar_encr = {'A':'D', 'B':'E', 'C':'F', 'D':'G', 'E':'H', 'F':'I', 'G':'J', 'H':'K', 'I':'L', 'J':'M',
+    'K':'N', 'L':'O', 'M':'P', 'N':'Q', 'O':'R', 'P':'S', 'Q':'T', 'R':'U', 'S':'V', 'T':'W', 'U':'X', 'V':'Y', 'W':'Z',
+    'X':'A', 'Y':'B', 'Z':'C'}
+    newtext = ""
+    for letter in range(len(plaintext)):
+        newtext += caesar_encr.get(plaintext[letter])
+    return newtext
+
+def decrypt_caesar(ciphertext):
+    """
+    Decrypts a ciphertext using a Caesar cipher.
+    First the ciphertext is converted into upper case. Then according to the decryption dictionary,
+    it maps each letter from the ciphertext to its decrypted letter. It then returns
+    the decrypted string.
+    """
+    ciphertext = ciphertext.upper()
+    caesar_decr = {'A':'X', 'B':'Y', 'C':'Z', 'D':'A', 'E':'B', 'F':'C', 'G':'D', 'H':'E', 'I':'F', 'J':'G',
+    'K':'H', 'L':'I', 'M':'J', 'N':'K', 'O':'L', 'P':'M', 'Q':'N', 'R':'O', 'S':'P', 'T':'Q', 'U':'R', 'V':'S', 'W':'T',
+    'X':'U', 'Y':'V', 'Z':'W'}
+    newtext = ''
+    for letter in range(len(ciphertext)):
+        newtext += caesar_decr.get(ciphertext[letter])
+    return newtext
+
+def encrypt_vigenere(plaintext, keyword):
+    """
+    Encrypts plaintext using a Vigenere cipher with a keyword.
+    First it multiplies the keyword so that it is the same length as the plaintext. Then it takes the 
+     number of each letter the plaintext and its corresponding keyword's number. These numbers are added together,
+     and the encvrypted letter is assigned according to the vigenere dictionary.
+    Lastly it returns the encrypted string.
+    """
+    plaintext = plaintext.upper()
+    keyword = keyword.upper()
+    newtext = ''
+    vigenere_dict = {0:'A', 1:'B', 2:'C', 3:'D', 4:'E', 5:'F', 6:'G', 7:'H', 8:'I', 9:'J', 10:'K', 11:'L', 12:'M', 13:'N', 14:'O', 15:'P', 
+    16:'Q', 17:'R', 18:'S', 19:'T', 20:'U', 21:'V', 22:'W', 23:'X', 24:'Y', 25:'Z'}
+    encr_word = keyword * (len(plaintext)//len(keyword) + 1)
+    encr_word = encr_word[0:len(plaintext)]
+    for letter in range(len(plaintext)):
+        orig_num = ord(plaintext[letter]) - 65
+        mod_num = ord(encr_word[letter]) - 65
+        sum_num = (orig_num + mod_num) % 26
+        newtext += vigenere_dict[sum_num]
+    return newtext
+
+
+def decrypt_vigenere(ciphertext, keyword):
+    """
+    Decrypts ciphertext using a Vigenere cipher with a keyword.
+    First it multiplies the keyword so that it is the same length as the ciphertext. Then it takes the 
+    number of each letter in the ciphertext as well as the number of its corresponding keyword letter. 
+    We take the difference of the ciphertext number and the keyword number, and according to the vigenere_dict
+    we are able to decrypt the ciphertext. We then return the ciphertext.
+    """
+    ciphertext = ciphertext.upper()
+    keyword = keyword.upper()
+    newtext = ''
+    vigenere_dict = {0:'A', 1:'B', 2:'C', 3:'D', 4:'E', 5:'F', 6:'G', 7:'H', 8:'I', 9:'J', 10:'K', 11:'L', 12:'M', 13:'N', 14:'O', 15:'P', 
+    16:'Q', 17:'R', 18:'S', 19:'T', 20:'U', 21:'V', 22:'W', 23:'X', 24:'Y', 25:'Z'}
+    encr_word = keyword * (len(ciphertext)//len(keyword) + 1)
+    encr_word = encr_word[0:len(ciphertext)]
+    for letter in range(len(ciphertext)):
+        orig_num = ord(ciphertext[letter]) - 65
+        mod_num = ord(encr_word[letter]) - 65
+        diff_num = (orig_num - mod_num) % 26
+        newtext += vigenere_dict[diff_num]
+    return newtext
+
+
+def encrypt_railfence(plaintext, num_rails):
+    """
+    Encrypts plaintext using a railfence cipher.
+    This follows a pattern that's found in the railfence, where in the first and last rows
+    the gaps between each letter are equal. In all other rows, you can see it as two different
+    starting points, but with the same gap amount. Therefore the rows in between the first and last
+    row are made up of two lists which are then combined together. The gap between letters is calculated
+    as the number of rails multiplied by 2 minus 2. 
+    """
+    gap = num_rails * 2 - 2
+    newtext = ''
+    for i in range(num_rails):
+        if i == 0:
+            newtext += plaintext[::gap]
+        elif i == num_rails - 1 and i < len(plaintext):
+            newtext += plaintext[num_rails - 1::gap]
+        else:
+            if i < len(plaintext): 
+                vec1 = plaintext[i::gap]
+                vec2 = plaintext[gap-i::gap]
+                comb_vec = ''
+                for i in range(len(vec2)):
+                    newtext += vec1[i]
+                    newtext += vec2[i]
+                if len(vec1) > len(vec2):   #This is the case when vector 1 is longer than vector 2
+                    newtext += vec1[len(vec1) - 1]  #Vector 2 will never be longer than vector 1
+    return newtext
+
+def decrypt_railfence(ciphertext, num_rails):
+    """
+    Decrypts ciphertext using a railfence cipher.
+    Unfinished....
+    """
+    gap = num_rails * 2 - 2
+    newtext = ''
+    lengths = []
+    groups = []
+    for i in range(gap):
+        if i < len(ciphertext):
+            lengths[i] = (len(ciphertext)  - i)/ gap + 1
+
+    for i in range(num_rails):
+        if i == 0:
+            groups[i] = lengths[0]
+        elif i == num_rails - 1:
+            if i < len(ciphertext):
+                groups[i] = lengths[num_rails - 1]
+        else:
+            if i < len(ciphertext):
+                groups[i] = lengths[i] + lengths[gap - i]
+
+    return newtext
+
+
+def read_from_file(filename):
+    """
+    Reads and returns content from a file.
+    It uses file I/O to read a file with read-only permission. 
+    It then returns the content found in the file.
+    """
+    with open(filename, 'r') as f:
+        content = f.read()
+    return content
+
+
+
+def write_to_file(filename, content):
+    """
+    Writes content to a file.
+    It uses file I/O to write the transformed text into the specified file.
+    """
+    with open(filename, 'w') as f:
+        f.write(content)
+
+
+def run_suite():
+    """
+    Runs a single iteration of the cryptography suite.
+
+    Asks the user for input text from a string or file, whether to encrypt
+    or decrypt, what tool to use, and where to show the output.
+    """
+    print("*Input*")
+    filetype = input('(F)ile or (S)tring? ')
+    original = ''
+    if filetype == 'F' or filetype == 'f':
+        filename = input('Enter the file to encrypt or decrypt: ')
+        original = read_from_file(filename)
+        original = original.replace(" ", "")
+    if filetype == 'S' or filetype == 's':
+        string = input('Enter the string to encrypt or decrypt: ')
+        original = string
+        original = original.replace(" ", "")
+
+    print("*Transform*")
+    mode = input('(E)ncrypt or (D)ecrypt? ')
+    method = input('(C)aesar, (V)igenere, or (R)ailfence? ')
+    transformed = ''
+    if mode == 'e' or mode == 'E':
+        if method == 'v' or method == 'V':
+            passkey = input('Passkey? ')
+            transformed = encrypt_vigenere(original, passkey)
+        elif method == 'R' or method == 'r':
+            rails = input('Number of rails? ')
+            rails = int(rails)
+            transformed = encrypt_railfence(original, rails)
+        elif method == 'C' or method == 'c':
+            transformed = encrypt_caesar(original)
+
+    elif mode == 'D' or mode == 'd':
+        if method == 'v' or method == 'V':
+            passkey = input('Passkey? ')
+            transformed = decrypt_vigenere(original, passkey)
+        elif method == 'R' or method == 'r':
+            rails = input('Number of rails? ')
+            rails = int(rails)
+            transformed = decrypt_railfence(original, rails)
+        elif method == 'C' or method == 'c':
+            transformed = decrypt_caesar(original)     
+
+
+    print("*Output*")
+    outputtype = input('(F)ile or (S)tring? ')
+    outputname = ''
+    if outputtype == 'F' or outputtype == 'f':
+        outputname = input('Filename? ')
+        write_to_file(outputname, transformed)
+        print('Transformed text written to ' + outputname)
+    if outputtype == 'S' or outputtype == 's':
+        print('The transformed text is:' + transformed)
+
+
+# Do not modify code beneath this point.
+def should_continue():
+    """
+    Asks the user whether they would like to continue.
+    Responses that begin with a `Y` return True. (case-insensitively)
+    Responses that begin with a `N` return False. (case-insensitively)
+    All other responses (including '') cause a reprompt.
+    """
+    choice = input("Again (Y/N)? ").upper()
+    while not choice or choice[0] not in ['Y', 'N']:
+        choice = input("Please enter either 'Y' or 'N'. Again (Y/N)? ").upper()
+    return choice[0] == 'Y'
+
+
+def main():
+    """Harness for the Cryptography Suite"""
+    print("Welcome to the Cryptography Suite!")
+    run_suite()
+    while should_continue():
+        run_suite()
+    print("Goodbye!")
+
+
+if __name__ == '__main__':
+    """This block is run if and only if the Python script is invoked from the
+    command line."""
+    main()

desmondw-assign1/feedback.txt

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+Name: <YOUR NAME>
+1) How long did this assignment take you to complete?
+
+
+
+2) What has been the best part of the class so far?
+
+
+
+
+
+3) What can we do to make this class more enjoyable for you?
+
+
+
+
+
+4) What types of assignments would excite you in this class?
+
+
+
+
+

desmondw-assign1/railfence-cipher.txt

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+WECRLTEERDSOEEFEAOCAIVDEN

desmondw-assign1/railfence-plain.txt

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+WE ARE DISCOVERED. FLEE AT ONCE

desmondw-assign1/secret_message.txt

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+KHOORZRUOG

desmondw-assign1/vigenere-cipher.txt

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+LXFOPVEFRNHR

desmondw-assign1/vigenere-plain.txt

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+Attack At Dawn!